1. Field of the Invention
The present invention relates to power tools and, more particularly, to an inertially actuated brake for a power tool.
2. Prior Art
Bidanset U.S. Pat. No. 3,923,126 discloses an inertial-manual actuated chain brake for a chain saw. As described in this prior art patent, the widespread use of portable power tools in the construction, lumbering, and consumer markets has emphasized the need for effective chain brakes. Lighter weight, reduced vibration, and higher power have resulted in very efficient cutting tools that are used in increasing applications by skilled and semi-skilled operators and, as with any powered machine, they present a potential hazard to the user. In the case of chain saws, a potential hazard is presented by the phenomenon known as "kickback." A "kickback" can be produced by a chain saw when the cutting elements on the chain momentarily stop cutting and is seized by the work material. The kinetic energy of the chain normally used to remove the material is suddenly transferred to the guide bar imparting a force to the guide bar that causes it to kick up; potentially towards the operator. Among other factors, the magnitude of the "kickback" force is generally related to the speed of the chain and the nature of engagement of the chain with the work material.
U.S. Pat. No. 3,923,126 relates to a chain brake that not only allows for manual braking, but also provides an inertia chain brake. This brake comprises the hand guard member of the chain saw being adapted to be moved relative to the rest of the chain saw in the event of a kickback of suitable acceleration and direction. This relative movement is caused by the inertia of the hand guard member.
A problem exists in the prior art in that hand-held power tools, such as a chain saw disclosed in U.S. Pat. No. 3,923,126 having acceleration activated inertia brakes using the weight of a hand guard as an inertia mass, requires that different hand guards be used for different types and models of tools, such as when comparing a large, long, and heavy chain saw versus a small, short and light chain saw. This, of course, can be expensive for a manufacturer having to design and to inventory all of these different types and models of hand guards.
Another problem that exists in the prior art is in regard to specifications dictated by governmental agencies. Because the governments of countries around the world have not adopted a uniform specification in regard to inertia brakes for power tools, there are different specifications for such tools throughout the world. Thus, even though a manufacturer may desire to sell the same model of power tool in two different countries, because of different specifications in such countries, it would be necessary to provide different hand guards for the same model power tool. In addition, because inertial-manual brakes for power tools are relatively new, some countries are still developing and modifying specifications. Thus, inertial-manual brake hand guards are constantly having to be redesigned to meet new or modified standards.
A further problem exists in the prior art in that inertial-manual brake hand guards in the past were made of a uniform material having a suitable density, such as metal, which is relatively expensive when compared to other materials, such as a thermoplastic material. In addition, the process of manufacturing such hand guards made of metal is more expensive when compared to thermoplastic molding techniques.
It is therefore an object of the present invention to provide a new and improved inertial-manual brake and hand guard for use with power tools.